The present invention relates to a rubber composition for tire tread.
Recently because of increasing social demand for reduction of fuel consumption of cars, in the development of low fuel consumption tires which have decreased rolling resistance, it has been generally attempted to decrease hysteresis loss of a rubber composition for tread. In the method to decrease the hysteresis loss, it is known that reduction of an amount of carbon black in the rubber composition for treads and use of silica as a filler are effective.
However decreasing the amount of carbon black increases the electric resistance of the rubber composition for treads, and thus an electric resistance of a tire obtained by using such a rubber composition for treads also becomes high. As a result, static electricity accumulates on the car body and tire, which causes radio noise and sparking at the time of filling fuel oil. Therefore, with respect to a rubber composition containing silica, in which the amount of carbon black is small, how the electric resistance is decreased is important.
The present inventors have found that the electric resistance can be decreased effectively when a specific diester of adipic acid is mixed to a rubber composition prepared by adding silica, and have completed the present invention.
For example, JP-A-60-223840, JP-A-61-66733, JP-A-63-43937, JP-A-1-242644 and JP-A-7-292154 disclose techniques to add an adipic acid ester as a plasticizer to a rubber composition. However, since only carbon black is used as a filler, a technique for decreasing electric resistance is not discovered and there is no disclosure and teaching with respect to the use of a diester of adipic acid for decreasing the electric resistance.
Namely, an object of the present invention is to obtain a rubber composition for treads which contains silica and has a low electric resistance. A further object of the present invention is to obtain a rubber composition for treads which contains silica and has well-balanced characteristics such as a low rolling resistance, abrasion resistance and good wet performance.